The subject invention relates to a method for reducing the scan line visibility in the display of a projection television receiver, which receiver includes three projection devices for projecting the three color signals red, green and blue, each projection device generating a raster of scanning lines, said rasters being converged with each other in superposition at a display screen for forming a desired display image.
Movie theaters have always had an advantage over television in that the theaters are able to present a life-size, or larger than life-size, image to the viewing public while television has been limited to small screen sizes, for example 19, 21 and 25 inches. However, with the advent of projection television, displays of 6-10 feet are now available to the consumer enabling one to have the benefit of a large screen display in one's own home.
While the images present on a standard television receiver are adequate, i.e. at a reasonable viewing distance, the scanning lines are for the most part indistinguishable, when these same images are then projected onto a large display screen in which the displayed image is, for example, ten times larger than that on a standard television receiver, the scanning lines become much more visible. This is in part due to the fact that the viewing distance is not increased to the same extent that the image is expanded.
Techniques have been suggested for reducing the scan line visibility in the projected image. These techniques include increasing the number of scan lines by various means of interpolation. However, in these techniques the projection television receiver must then output the lines at twice the normal sweep rate. This would require digital conversion of the signal, wider bandwidth video amplifiers and wider bandwidth deflection circuits, along with the inclusion of A/D and D/A converters and digital memory for at least three lines. Hence, the projection television receiver, which already is expensive, would become much more expensive.